In view of our increasing awareness that environmental carcinogens, such as polycyclic aromatic hydrocarbons, aflatoxins and nitrosamines, may be responsible for the production of certain cancers in man, it would be desirable to have a simple screening procedure to identify those individuals who are at an unusually high risk when exposed to such carcinogens and/or other environmental pollutants. Kapitulnik et al., Clin. Pharmacol. Therap. 20, 557 (1976) have suggested that such screening might be possible by determining the plasma half-life of drug which is metabolized by the same enzyme system(s) that metabolizes the environmental pollutant. One such drug which might serve this purpose is zoxazolamine (2-amino-5-chlorobenzoxazole). Kapitulnik et al., supra, have recently demonstrated that there is a highly significant correlation (r=0.98:p &lt;0.001) between the hydroxylation of benzo[a]pyrene (BP), a known carcinogen, and zoxazolamine in the placentas from smokers and non-smokers which suggests that BP and zoxazolamine are metabolized in the human placenta by the same enzyme system or by different systems which are under similar regulatory control. A somewhat weaker relationship has been found between BP and zoxazolamine metabolism in the human liver, Kapitulnik et al., Clin. Pharmacol. Therap. 21, 166 (1977). Furthermore, Kellerman et al., Am. J. Hum. Genet. 25, 327 (1973), using human lymphocytes, have shown a positive correlation between the occurrence of bronchogenic carcinoma and an individual's capacity to metabolize BP.
With these facts in mind, a simple and rapid method is required for the determination of the plasma half-life of zoxazolamine if the latter is to be used as a screening procedure in the general population. The technique of immunoassay, particularly radioimmunoassay (RIA), by virtue of its simplicity, would satisfy this requirement.
U.S. Pat. No. 3,988,430 discloses a radioimmunoassay for antipyrine whose half-life in a subject has been correlated with the genetically controlled level of benzo[a]pyrene hydroxylase induction. The latter measurement has been associated with risk to bronchogenic carcinoma.